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Thursday, July 14, 2016

Laser Tube: Protecting, Operating, Cooling & Repairing

Cooling, Operating and Protecting The Laser 

These are optical and cooling techniques I have been collecting. Some I have tried and some not.
You use these at YOUR OWN RISK.


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After flailing for a few days with what I thought was a bad power supply or tube it dawned on me that I had never used distilled water (I am always tearing it apart and how conductive can the water be anyway?) and I knew that I had some algae in the tank.

I knew better from listening to others but seriously arching through the glass jacket through the water to gnd in the tank? You better believe it, I have now proven it, to my satisfaction that is. I should have known better because I worked with someone that was blowing supplies every month and it turned out to be CAR antifreeze (that's definitely a no-no).

The symptoms was an intermittent screeching noise when the laser was in operation. It did not do it continuously and it did not do it every time.
I thought it was coming from the LPS and finally was about to conclude that it was a failing winding inside the fly-back transformer. What bothered me was I could see no evidence of an arc even in a dark room. 

What I did notice was the flux beam shifting and changing shape at the anode end.

So I cleaned the system put in distilled water (3 Gal) and RV antifreeze (1/2 gal), powered it up and from then on no screeeeeeching just smooth wood smoking power. 

I wonder how many good supplies and tubes have been replaced or fry'd do to this problem.

The Simplest Cooling System Approach

"The simplest and safest for humans and machines it to use pure distilled water in a closed system which prevents contaminates that might encourage algae growth. Change water every 6 months with other maintenance." 

From +Arthur Wolf 

The underlying principle is that pure uncontaminated distilled water does not grow algae.

Conductivity Data

Here is some actual data. I don't know why I never thought of measuring this before. I wish I had measured the water before emptying it.
I used a HM Digital COM 100.
The temp was about 60F-65F
Distilled water = 2.6 uS
Distilled/RV mix:6:1 = 142 uS
RV antifreeze = 414 uS
Don's tap = 370 uS Prestone (ethelene glycol) = 633 uS
Vinegar: 137 uS
"Purified" water: 10uS
Aquarium algaecide: TBD

uS = micro-siemens

Algaecide for Algae Prevention

Algaecide: Tetra Algea Control
Active ingredients: 5% Poly [Oxyethylene (Dimethyliminio) Ethylene (Dimethylimino)
Ethylene (Dimethylimino) Ethylene Dichoride]
Recommended dose for Aquariums: 1ml per 12 gallons, 1 drop (.084ml) per 1 gal (3.8L)
Conductivity measurements: 1 drop added to 1 gallon of fresh distilled water.
  • Reading before algaecide control = 4.8uS
  • Reading after adding algaecide = 4.9 uS
Conclusions: this brand of algae-cide does not raise the conductivity of distilled water. (continuing tests to be conducted).
Expectations: adding 5 drops, (.42ml) per 5 gallon bucket of distilled water will not increase the conductivity of the water but will prevent algae growth.

Clorox for Algae Prevention

Clorox: mostly sodium hypochlorite

Sodium Hypochlorite Conductivity (note: these measurements were made with an ohmmeter and that will not work so do not use this data). A meter will not work to measure conductivity because DC polarizes the solution. AC is used to solve this problem so insure your meter or measurement method uses AC.

Here is a better method for calculating.

Estimating Practical use of chlorine:

How much Clorox needed to kill algae?

1/4 teaspoon per gallon of water = .042 oz/gal
.042 * 5 = .21 oz/5 gal = 6.2 ml/5 gallons

Measurements to attain conductivity at relevant concentrations:

  1. 2.5 gallons distilled water was added to bucket. Conductivity = 2.2 uS
  2. Added 3 ml Clorox. Conductivity = 44.9 uS
  3. Added additional 2.5 gallons. Conductivity = 22 uS
  4. Added 3 ml Clorox. Conductivity = 46 uS

Final (for now) formula:

Mix 6 ml of Chlorox with 5 gallons of water and expect the conductivity to be in the 40's uS.

Long Term Testing of Water Conductivity

I started a test of tap water conductivity to see what the conductivity does over time and as algea grows. I am also monitoring my main tank (B).

Test setup:
A. Water in bucket: from my tap sitting indoors in open container
B.  Water in my K40 tank

My K40 tank (B) has the formula from above.

Tracking my water conductivity over time

Lens focus, orientation & cleaning:


Flow Sensor


The loss of cooling water will certainly cause damage to the laser and the laser power system. Every system should have a flow sensor plumbed in series with the pump and the lasers cooling jacket.
The sensor that I use is:

This sensor needs to be installed on the output side of the laser. I made a hanger to hold it upright on the side of a 5 gal bucket. This way it insures that water is flowing out of the laser and it can detect any leaks from the pumps output to the sensors input.

Electrical connections;

The flow sensor is connected in series with the interlock circuit and in effect stops the laser from firing if there is no flow. 
See Build Schematics  for full machine details

If you for some reason do not want to add a sensor at least insure that the pump comes on with the machine. You can simply plug the pump and machine into the same power strip and turn them both on at the same time.

The End of My Tube Fell Off!

If you did not install a water sensor then at some point the pump will not be on, due to failure or  simply forgetting to turn it on, and the tube will overheat.

If the tube overheats the water jacket on the end of the tube can de-laminate and fall off.

Apparently if you are careful to keep it off the optical output area of the jacket you can use EPOXY it back on. I would surmise that high temp epoxy would be best.

Temperature Monitoring

The laser must stay within its coolant operating range if it is to operate consistently and reliably. The cooler the laser is kept the more power it will be capable of. The power capacity of the laser will change with temperature therefore it is important to monitor the water temperature and prevent the laser from operating is the temp gets to high.
Install temperature monitoring electronics such as:

This device's relay contacts (NC) is also wired in series with the interlock circuit and will disable the laser from firing if the temperature is to high or low. The probe is put into the bucket near the output or the flow sensor.
See Build Schematics  for details.

This controller can be set up to produce an audible alarm outside of its set-points. (See the manual). I mounted it on thr front of the machine but plans are to move it up to the control panel later. The unit requires 12VDC so an additional supply is needed. Before I installed the 12V supply in my conversion I used a 12V brick plugged into a power strip. 

Laser Tube Operation and Failure

Laser tube operating conditions (Reci Laser):

  • Water cooling: using purified water; 2 to 5 liter/minute, (31GPH-80GPH)
  • Water temperature: 10-40℃, (50F - 104F)
  • The operating environment: temperature 2-40℃,(35.6F - 104F; humidity 10-60%.
  • The working current: test current is 29mA. Maximum working current is 29mA. The running current must be kept below 27mA. The life span can reach 8,000 hours if the current is kept below 25mA.
  • The ammeter must be connected to the negative electrode of laser tube.When it is working under over high current for long term, the negative pole will appear light yellow and the life span will be shortened rapidly.
  • To protect dust from going into the insulation sheath, please wrap it with plastic film.

Laser Tech Tips

InstallationTube Installation

Specs for Engraving function:

"When the working current is 4mA and the tube is in the state of pre-ionization
the laser can be used for high-frequency impulse engraving. [I think this means that the tube ionizes above 4ma. The stock K40 engraves by dithering the image (converts to dots) and that it can create dots above 4ma] "

Parallax: Laser failure modes and warranty for one vendor: 

Various Cooling-water treatments:

  • To keep out algae use a teaspoon of granulated chlorine to 5 gal.
  • To help with bubbles one drop of dish detergent.
  • 1 part RV antifreeze to 3 parts distilled water (kills algae, keeps water from freezing)
  • Diluted Dowfrost
  • Aquarium Algecide

Cleaning the laser tube water jacket

Replace all the water in reservior with a couple of litres of vinegar and tap water... let it run for 12-24 hours replace all water with tap water only let it run for a bit... place outlet tube into a waste pan and flush adding a bit more tap water as your reservoir drains... purge all water and replace with distilled water and some algaecide drops for aquariums

Water Pumps

From +Scott Marshall :"When all is well, the stock system should fill a 1 gallon jug about 1/2 full in 60 seconds. About 1/2 gpm or 2 Lpm. .................. the Little Giant PE-1 is a good quality replacement pump which is just right for the k40 and available worldwide."